Advanced water treatment system and advanced water treatment method

ABSTRACT

An improved method for water treatment which comprises subjecting a water to be containing a hazardous material such as a dioxin or PCB to an ozone treatment contacting the water with fine bubbles of ozone having an average diameter of 0.5 to 3 microns; and a combination of the ozone treatment with one or more of a hydrogen peroxide treatment, a UV radiation treatment, an electrolysis treatment and a treatment with a carbonaceous filter material. The above ozone treatment or combination of treatments can be used for surer realization on of an intended effect of a water treatment, which is difficult to achieve by the use of a conventional method wherein ozone or hydrogen peroxide is simply mixed with a water to be treated. In particular, the combination of treatments leads to a more improved effect of water treatment.

TECHNICAL FIELD

This invention relates to an advanced water treatment technique foroxidative destruction of harmful substances typified by environmentalhormones, such as dioxins and PCB, by using the strong oxidation powerof ozone.

BACKGROUND OF THE INVENTION

Today, we face the growing problem of how to deal with harmfulsubstances, such as environmental hormones, on the earth. Dioxins aretypical examples of harmful substances. It is reported that dioxinsgenerated in Japan (those generated by incinerator plants of itsmunicipalities alone) amount to 2,800 grams (fiscal 1998). To cope withthis problem, controls of incinerator plants, sources of generation ofdioxins, are being made stricter so as to limit the amounts of dioxinsgenerated thereat.

However, restrictions alone on the generation of dioxins is notsufficient for reduction of the amount of dioxins present in theenvironment, because once they are generated, they circulate through theenvironment without being destroyed. Therefore, unless dioxinscirculating in the environment are destroyed to thereby end theircirculation while the amount of generation thereof is restricted, thewhole amount of dioxins in nature cannot be decreased.

For instance, dioxins circulate in the environment as follows: Dioxinsonce released from an incinerator plant contaminate food, such asagricultural, livestock and fishery products, enter human bodies via thefood, and then are discharged as wastes from human bodies into theenvironment. Those wastes containing harmful substances, such asdioxins, are collected in human wastes treatment facilities and publicsewage works, or put together in single or joint private sewage systemsall over the country and flow therefrom into rivers and then into thesea.

As described above, dioxins collected in human wastes treatmentfacilities or public sewage works via human wastes are released into theenvironment without being decomposed. Harmful substances released intothe environment repeatedly return to human bodies via fishery productsand the like while being increased in concentration. As describedhereinabove, unless the vicious circle in the circulation of dioxins isbroken anywhere, adverse influences of dioxins present in theenvironment on human bodies cannot be reduced even if only the amount ofgeneration of dioxins is restricted.

The ozone treatment and the hydrogen peroxide solution treatment areknown as techniques of decomposing harmful substances present in waterto be treated. According to these treatments, it is true that harmfulsubstances were subjected to oxidative destruction to some purpose, butalmost all of these techniques only mix ozone and hydrogen peroxidesolution with water to be treated, or simply agitate the resultingmixture. Therefore, it cannot be necessarily said that they are capableof fully achieving the effects of destroying harmful substances. Evennow, harmful substances, including dioxins, continue to increase inwater systems in the environment, and hence the advent of a new advancedwater treatment technique has been desired which promises more excellenttreatment effects.

DISCLOSURE OF THE INVENTION

The present invention has been made in order to meet the above-describeddemand. That is, an object of the present invention is to provide anadvanced water treatment technique that does not simply make use ofozone, differently from the conventional water treatment technique, butis based on an ozone treatment which is capable of braking a viciouscircle of harmful substances, such as dioxins, through wastes dischargedfrom human bodies, by providing more advanced treatment effects.

To attain the above object, the advanced water treatment processaccording to the present invention is based on an essential treatmentprocess for bringing minute bubbles of ozone having an average particlediameter (bubble diameter) of e.g. 0.5 to 3 μm into contact with waterto be treated, which contains harmful substances, such as dioxins andPCB, thereby carrying out the ozone treatment for oxidative destructionof the harmful substances contained in the water. In a more concreteform, an advanced water treatment system of the present invention ischaracterized by comprising an ozone treatment device for bringingminute bubbles of ozone having an average particle diameter (bubblediameter) of e.g. 0.5 to 3 μm into contact with the water to be treated,in a retentive manner, thereby carrying out oxidative destruction of theharmful substances.

According to this advanced water treatment process and system, ozone isnot simply supplied to the water to be treated but minute bubbles ofozone are supplied to the water to be treated. More specifically, eachminute bubble of ozone has a very small buoyant force, and hence ozonecan be caused to stay within the water for a much longer time period.Further, areas of ozone brought into contact with the water can be madeby far the larger. As a result, differently from the conventional watertreatment process in which aeration is simply carried out with ozone,the efficiency of oxidation of harmful substances dissolved in the watercan be dramatically improved.

The “water to be treated” for treatment by the advanced water treatmentprocess and system of the present invention includes water at highpollution levels, such as waste water containing sludge and soil, humanexcreta, sewage water containing excreta of domestic animals, householdwaste water, clinical waste water, papermaking waste water, andindustrial liquid waste, and water at low pollution levels, such aswater in rivers or lakes, water used in bathhouses, swimming pools, andthe like. In short, since the treatment is intended for decomposingharmful substance, so long as the water to be treated contains harmfulsubstances, the kind of a pollution source does not matter.

Further, the harmful substances which can be decomposed include dioxins,PCB, and other environmental hormones. It goes without saying that thepresent process and system is capable of sterilizing infective diseasesuch as Escherichia coli, salmonella, and mad cow disease.

Further, the advanced water treatment system may be of a fixed type, oran in-vehicle mobile type, but is characterized by the capability ofcontinuous treatment.

As described hereinabove, the ozone in the form of minute bubbles has avery small buoyant force and stays within the water for a very long timeperiod. Therefore, there is a difficulty that if only the minute bubblesof ozone are simply supplied to the ozone treatment tank, it takes muchtime for the ozone to be uniformly diffused throughout the water withinthe tank, and hence the high oxidative destruction power of the ozonerealized in the form of minute bubbles is not fully made use of.Therefore, in the water treatment process of the present invention, asone method of evenly diffusing the minute bubbles of ozone, the minutebubbles are supplied to a water pipe which is provided for connectingeach treatment tank arranged within a treatment system. The water isflowing violently through the water pipe, so that ozone formed intominute bubbles by “ozone supply means” comprised of an ozone generatorand an ozone bubble-forming device (line mixer type, or vortex flowturbine pump type) is supplied to the water flowing through the waterpipe, whereby the minute bubbles of ozone are injected into the ozonetreatment tank in a gushing flow and evenly diffused throughout theinside of the tank.

Further, in another method of diffusing the minute bubbles of ozone, anozone treatment tank for bringing the minute bubble of ozone intocontact with the water to be treated in a retentive manner is providedwithin the treatment system, and the ozone is blown from the bottom ofthe tank into the water within the tank to cause a forced convection ofthe water. In other word, an ozone treatment tank for bringing theminute bubbles of ozone into contact with the water to be treated in aretentive manner is provided within the treatment system, and the waterwithin the tank and the minute bubbles of ozone supplied from the ozonegenerator are vigorously moved around to produce a forced convectionstate of the water. An ozone treatment device using the ozonebubble-forming device (rotational type) arranged at the bottom of theozone treatment tank carries out the ozone treatment. In this case, thewater to be treated and ozone are vigorously turned around to blowminute bubbles of ozone having an average particle size of 10 to 20 μm,or 50 to 60 μm, into the water in the tank.

Further, the advanced water treatment process and device may use oneozone treatment tank, but if a plurality of ozone treatment tanks arearranged at successive respective stages, they can provide enhancedoxidative destruction effects. Further, when the plurality of ozonetreatment tanks are provided, the tanks should not be simply arranged atrespective successive stages, but it is preferred that extra ozonecoming up from the water within the latter-stage ozone treatment tank iscaused to be circulated to the former-stage ozone treatment tank foreffective utilization of ozone.

Further, the advanced water treatment process and system is capable ofperforming oxidative destruction of almost all harmful substances in thewater to be treated, by utilizing the minute bubbles of ozone. However,the present invention further performs a desired combination of ahydrogen peroxide solution treatment, an electrolysis treatment, anultraviolet radiation treatment, and a carbonized filter medium contracttreatment (carbonized filter medium treatment) to thereby moreeffectively decompose the harmful substances.

One combination-type treatment provides an example suitable for advancedtreatment of waste water at relatively low pollution levels, includingwater from waterworks, swimming pools, and bathhouses, and water inrivers. In this example, the advanced water treatment process and systemis configured such that the ozone treatment, the ultraviolet radiationtreatment, and the carbonized filter medium contact treatment arecarried out in the mentioned order. It should be noted that theultraviolet radiation treatment decomposes harmful chlorides bydechlorination reaction through irradiation of ultraviolet rays. Thecarbonized filter medium treatment eliminates harmful substancesremaining untreated within the water by adsorbing them by a specialfilter medium.

The waste water to be treated here has a relatively low pollution load,and hence the ozone treatment can decompose almost all harmfulsubstances, but harmful substances which remain even after the ozonetreatment are treated or processed by the ultraviolet radiationtreatment. Then, the water to be subjected to the ultraviolet radiationtreatment contains ozone in the form of minute bubbles mixed therein bythe ozone treatment at the preceding stage, and hence hydroxyl radical(OH⁻) having a high oxidative power can be generated in a larger amountto provide high decomposition effects. Then, by carrying out thecarbonized filter medium contact treatment thereafter, heavy metals,such as aluminum, arsenic, and cadmium, contained in the water to betreated are adsorbed for elimination from the water. As the carbonizedfilter for use in the treatment, the use of a conifer carbonized filtermaterial obtained by carbonizing raw materials of a plurality of kindsof conifer, including cedar, pine, and Japanese cypress (hinoki) at ahigh temperature range of 800 to 900° C. enhances absorptive action ofthe medium to a very high degree. By subjecting the water to theabove-mentioned sequence of treatments, it is possible to obtain waterwhich is purified to a quality level suitable for drinking water.Further, this treatment process and system can attain sufficienttreatment effects by relatively simple treatment, and the costs thereforcan be held at a low level.

Another combination-type treatment provides an example suitable foradvanced treatment of waste water having a relatively high pollutionload, such as human excreta, sewage water, and waste water fromagricultural community. In this example, the advanced water treatmentprocess and system is configured such that the hydrogen peroxidesolution treatment, the ozone treatment, the ultraviolet radiationtreatment, and the carbonized filter medium contact treatment arecarried out in the mentioned order. It should be noted that the hydrogenperoxide solution treatment admixes the hydrogen peroxide solution as aliquid in the water to be treated, whereby microorganisms are sterilizedand the harmful substances are oxidized, by the oxidative power of thehydrogen peroxide solution.

The waste water treated in this example have relative high pollutionloads, and are required to treat human excreta. Therefore, the hydrogenperoxide solution treatment for processing foul odor and human excretaresidue is carried out prior to the ozone treatment. In this case, it isadvantageous that the foul-odor air generated from the water to betreated within the treatment system is mixed into the hydrogen peroxidesolution as minute bubbles having an average particle diameter ofapproximately 0.01 to 0.2 mm, for oxidative destruction thereof. Byforming the foul-odor air into the minute bubbles, the oxidativedestruction thereof by the hydrogen peroxide can be carried out withhigh efficiency. In respect of high-efficiency treatment, it is moreadvantageous that pH of the water to be treated is adjusted to 8 to 10in advance, and still further advantageous that at least one of gold,copper oxide, and iron oxide is thrown into the water, for promotion ofthe oxidative treatment by the hydrogen peroxide. Then, after thehydrogen peroxide solution treatment, the ozone treatment, theultraviolet radiation treatment, and the carbonized filter mediumcontact treatment are carried out, whereby the water to be treated canbe purified to a quality level suitable for drinking water.

A still another type of the treatment is an example suitable foradvanced treatment of waste water containing harmful heavy metals, suchas industrial liquid waste from a particular factory, and waste waterfrom a final waste disposal plant. In this example, the advanced watertreatment process and system is configured such that the hydrogenperoxide solution treatment, the electrolysis treatment, and the ozonetreatment are carried out in the mentioned order. It should be notedthat the electrolysis treatment is one which is executed for eliminatingheavy metals, such as arsenic, cyanogen, aluminum, cadmium, and thelike, which cannot be decomposed by oxidative treatment ordechlorination treatment.

Since the waste water treated here contains heavy metals, theabove-mentioned hydrogen peroxide solution treatment is carried out, andthen the electrolysis treatment is carried out. This enables theelectrolysis treatment to be carried out with high efficiency owing tohydrogen peroxide solution remaining within the water subjected to thehydrogen peroxide solution treatment. After the heavy metals are thuseliminated, the above-mentioned ozone treatment is carried out wherebythe water to be treated can be purified to a quality level suitable fordrinking water.

As the tank for carrying out the ultraviolet radiation treatment, it isadvantageous that an ultraviolet radiation treatment tank is providedwhich has an ultraviolet light source and inner walls coated withtitanium dioxide, and it is further advantageous to carry out aphotocatalytic treatment by irradiating ultraviolet rays to the innerwalls to consume the foul odor in combination with the ultravioletradiation treatment. This can more efficiently enhance the efficiency ofdecomposing the harmful substances by hydroxyl radical. The ultravioletradiation treatment tank can be configured such that it has a pluralityof partition walls coated with titanium dioxide, with partition wallsbeing arranged such that the distance between adjacent ones of thepartition walls is within 30 cm. More specifically, the ultravioletradiation treatment tank has a body in the form of a bottomed hollowcylinder extending vertically, an ultraviolet lamp being arranged in adiametrical center of the body, with the plurality of partition wallshaving plate surfaces radially extending toward the ultraviolet lamppositioned in the center of the arrangement of partition walls. Thisenables the electrons causing photocatalytic action to be dispersedevenly throughout the inside of the treatment tank, whereby thephotocatalytic effects can be fully provided.

Although each of the above-mentioned types is composed of a sequence oftreatments, this is not limitative, but it goes without saying the foreach treatment stage, a settling tank may be provided for carrying outthe settling treatment, to thereby eliminate impurities contained in thewater to be treated.

Further, an aeration treatment may be carried out for a biologicaltreatment of organic contaminants contained in the water to be treated.

In all of the above-mentioned cases, treated water obtained by theadvanced water treatment process and system ensures a water quality at alevel higher than a level satisfying 26 drinking water-suited waterquality criteria defined by the Japanese food sanitation law.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an advanced water treatment system(facility) of a fixed type, according to an embodiment of the presentinvention;

FIG. 2 is a diagram showing an advanced in-vehicle water treatmentsystem (facility) according to another embodiment of the presentinvention; and

FIG. 3 is a plan view showing the arrangement of the advanced in-vehiclewater treatment system appearing in FIG. 2.

DESCRIPTION OF REFERENCE NUMERALS

1 aeration, tank

2 hydrogen peroxide solution treatment tank

3 partition wall (net)

4 storage tank

5, 6 ozone treatment tank

7 a silent discharge ozone generator

7 b ozone bubble-forming devices

8 waste ozone-disposal treatment device (detoxification device)

9 ultraviolet radiation treatment tank

10 pH adjustment tank

11 retention tank

12, 13 electrodes

14 carbonized filter medium

15 large-sized truck

16 storage tank

17 vacuum generator

18 generator unit

19 screen

20, 21 ozone treatment tank

22 a ozone generator

22 b ozone bubble-forming devices

23 waste ozone-disposal treatment device

24 ultraviolet radiation treatment tank

25 carbonized filter medium treatment tank

26 retention tank

27 carbonized filter medium

W waste water

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail with reference toFIG. 1 showing an embodiment thereof. FIG. 1 is a diagram showing afacility of a fixed type including an advanced water treatment systemaccording to the present invention. An aeration tank 1 is a tank intowhich waste water W containing human excreta is first thrown by a vacuumcar and the like. In this aeration tank 1, minute bubbles ofapproximately 0.01 to 0.02 mm in diameter are breathed in from below forsettling and separating foreign matters (hardened materials). Bybreathing minute bubbles into the aeration tank 1 as described above, itbecomes possible to prolong a time period for holding minute bubbles inwater, and increase a contact area of air with water to be treated,thereby making it possible to enhance efficiency of oxidization oforganic substances dissolved in the water. Further, in the aeration tank1, slaked lime is thrown into the waste water W for alkalization of thesame.

Arranged in a manner adjacent to the aeration tank 1 is a hydrogenperoxide solution treatment tank 2 for carrying out a hydrogen peroxidesolution treatment. There is provided a partition 3 in the form of a netbetween the tank 2 and the aeration tank 1 such that the foreignmaterials are prevented from entering the tank 2. The waste water Whaving a pH adjusted to 8 to 10 is moved into the tank 2, and an aqueoushydrogen peroxide solution is poured into the tank 2. It should be notedthat the waste water W is alkalinized in advance since the alkalizationcontributes to enhancement of the oxidizing and decomposing power of theaqueous hydrogen peroxide solution. Slaked lime, for instance, issuitable for a pH adjuster. Similarly to the aeration tank 1, in thehydrogen peroxide solution treatment tank 2 as well, minute bubbles arebreathed in from below, and hence the aqueous hydrogen peroxide solutionpoured in is mixed with the waste water W by the agitating effect of theminute bubbles. This is because it is preferable to mix waste water Wwith the hydrogen peroxide solution by air agitation. When the aqueoushydrogen peroxide solution is mixed with the waste water W, oxygen (O)is released, and the oxygen can perform oxidative destruction of harmfulsubstances, such as dioxins and the like, contained in the waste waterW. In order to increase a deodorizing effect of the hydrogen peroxidesolution treatment tank 2, the inner surfaces of an upper part of thetank 2 are coated with titanium dioxide, and a fluorescent light isarranged on a ceiling portion of the tank 2. This is to cause titaniumdioxide to perform the photocatalytic function to thereby enhance thedeodorizing effect of the tank 2. Further, an electric fan is arrangedat an upper portion inside the tank 2, for stirring air within the tank,which contributes to reinforcement of the photocatalytic function.

The waste water W is once stored in a storage tank 4 after beingsubjected to the hydrogen peroxide solution treatment. The waste water Whaving passed through the storage tank 4 is fed to an ozone treatmentdevice which is comprised of ozone bubble-forming devices 7 b, an ozonegenerator 7 a, and ozone treatment tanks 5 and 6, for carrying out ozonetreatment. The ozone treatment is carried out in the ozone treatmentdevice. Inside the ozone treatment tanks 5 and 6, harmful substances,such as dioxins and the like, contained in the water to be treated areoxidized and decomposed by the oxidation force of oxygen generated fromozone gases. Although only one tank may be arranged as an ozonetreatment tank, normally, ozone treatment is carried out by using twoserially-connected ozone treatment tanks. One of the ozonebubble-forming devices 7 b which is connected to the silent dischargeozone generator 7 a is connected to a piping for guiding the waste water(piping for guiding water to be treated) arranged in the vicinity of aninlet of the ozone treatment tank 6 at a latter stage of the watertreatment system. From this ozone bubble-forming device 7 b, ozone gasesare supplied as minute bubbles of approximately 0.5 to 3 μm. The ozonegases breathed out from a lower portion of the latter-stage ozonetreatment tank 6 once stay at an upper portion of the tank 6, andthereafter fed to the other ozone bubble-forming device 7 b arranged ina piping in the vicinity of an inlet of the ozone treatment tank 5 at aformer stage of the water treatment system. Then, the ozone gases formedinto minute bubbles again are discharged into the former-stage ozonetreatment tank 5. Out of the ozone gases fed to the former-stage ozonetreatment tank 5, ozone stored in an upper portion thereof is releasedinto the atmosphere after being detoxified by a waste ozone-disposaltreatment device 8. This is for the purpose of making effective use ofozone. It should be noted that an amount of the ozone stored in theupper portion of the latter-stage ozone treatment tank 6 is equal toapproximately one-tenth of the amount of the ozone injected, and theozone bubble-forming device 7 b arranged in the vicinity of the inlet ofthe former-stage ozone treatment tank 5 may have a capacity equal toapproximately one-tenth of that of the ozone bubble-forming device 7 barranged in the vicinity of the inlet of the latter-stage ozonetreatment tank 6. Further, the water treatment system is configured suchthat for the transfer of ozone from the latter-stage ozone treatmenttank 6 to the former-stage ozone treatment tank 5, the concentration ofozone is detected, and the transfer of ozone is permitted when apredetermined concentration thereof is sensed. A waste ozone-disposaltreatment can be effected in the following manner: After minute particleof ozone remaining in the air collected in the upper portion inside theozone treatment tanks 5 is separated from the air by using a centrifugalseparator, a reverse osmosis membrane device, or a filter medium, theparticles of ozone are subjected to either a plasma incinerationtreatment or an adsorption treatment which is carried out by using aconifer special carbonized material made of a conifer which is producedthrough a high-temperature treatment of the conifer at temperaturesbetween 800° C. and 900° C. over a predetermined time period or longer.In this embodiment, the plasma incineration treatment is carried out.Further, the ozone generator 7 a used in this embodiment is a knownsilent discharge ozone generator, while the ozone bubble-forming device7 b is of a line mixer type which mixes ozone supplied from theconventional ozone generator 7 a with waste water W, and causes themixture of ozone and waste water W to simultaneously pass therethroughto thereby cause the minute bubbles of ozone to exist in water to betreated, by the stirring force of a line mixer thereof. According tothis process, it is preferred that the bubbles of ozone have a particlediameter (bubble diameter) of 0.5 to 3 μm. This is because a particlediameter larger than 3 μm reduces efficiency of the ozone treatment anda particle diameter smaller than 0.5 μm makes it difficult to diffuseozone bubbles into water to be treated, and requires an additional ozonediffusion device, such as an ultrasonic treatment device, therebyspoiling practicability of the ozone bubble-forming device 7 b. Further,the amount of injected ozone (amount of ozone brought into contact withwater to be treated) is determined depending on the amount of organicsubstances dissolved in water to be treated and the like. In thisembodiment, the amount of injected ozone is set to 0.004 to 0.0015 mg (4to 15 ppm) per liter of water to be treated, preferably 0.004 to 0.008mg. If the amount of injected ozone is smaller than 0.004 mg/liter, theeffect of injected ozone is reduced, while if the amount of injectedozone is larger than 0.015 mg/liter, the concentration of ozone in thewaste water is saturated, which makes useless the injection of ozone ata rate in excess of 0.015 mg/liter. By setting the size of ozone bubblesand the amount of injection of ozone as described above, it becomespossible to carry out a continuous treatment of water to be treatedwhich contains harmful substances, such as dioxins and the like, at apractical level, which could not be carried out by the conventionalwater treatment system. More specifically, conventionally, each bubbleof injected ozone has a size of approximately 0.2 to 0.3 mm in diameter,and hence the ozone injected is caused to rise to the surface of waterin an ozone treatment tank in several seconds. This results in anextremely short contact time period during which the ozone and the waterare brought into contact with each other. Consequently, to decomposeapproximately 80% of toxic substances, it was required to continueinjecting ozone in a large amount of 70 to 100 mg per liter of water tobe treated for 30 to 300 minutes by method. On the other hand, accordingto the present embodiment, the oxidation reaction and solubility ofozone are enhanced to respective very high levels by injecting ozonehaving a particle or bubble diameter of 0.5 to 3 μm in an amount of0.004 to 0.0015 mg per liter of water to be treated. This enables watertreatment to be carried out at high efficiency. If the water is treatedfor 2 minutes in a continuous-type ozone treatment tank, it is possibleto decompose approximately 80% of toxic substances. In the presentembodiment, ozone formed into minute bubbles having a particle or bubblediameter of 0.5 to 3 μm is brought into contact with the water to betreated. This makes it possible to oxidize and decompose harmfulsubstances at efficiency more than 100 times as high as that of theconventional water treatment system, and contributes to economicaladvantages including reduction of the initial costs and running costs ofthe treatment system, e.g. through downsizing of treatment devices usedtherein.

After having passed through the ozone treatment tanks 5 and 6, the wastewater W is transferred to an ultraviolet radiation treatment deviceformed of an ultraviolet radiation tank 9, wherein the waste water W isirradiated with ultraviolet rays having a wavelength of approximately180 nm to 310 nm. Ultraviolet radiation treatment is executed in theultraviolet radiation tank 9, and dioxins and the like can be decomposedthrough a dechlorination reaction by the ultraviolet radiation. Further,in this process, it can be expected that a hydroxyl radical (OH⁻) whichis by far stronger than ozone in oxidative power can be generated by thepresence of minute bubbles of ozone remaining in the waste water W inthe ultraviolet radiation tank 9, and the ultraviolet radiation, andtherefore, it can be expected that dioxins and the like which could notbe decomposed only by the preceding steps of the ozone treatment can bereliably decomposed.

To increase efficiency of decomposition of harmful substances, such asdioxins and the like, by ultraviolet rays, titanium dioxide is coated onthe inner surface of the ultraviolet radiation tank 9 to thereby employdecomposition using a photocatalyst in combination with the ozonetreatment. In this case, the traveling distance of electrons emittedfrom the titanium dioxide involved in photocatalysis is approximately 15cm, and hence when the ultraviolet radiation tank 9 is increased insize, it is required to divide the inside of the tank 9 such that thedistance between the respective partitions is 30 cm or less. To meet therequirement, in the present embodiment, an ultraviolet lamp is arrangedat a central axis portion of the cylindrical ultraviolet treatment tank.The ultraviolet treatment tank 9 is further provided with a plurality ofpartitions, not shown, which have surfaces coated with titanium dioxide.Each partition extends from a root end on an inner wall of theultraviolet treatment tank 9 to a distal end in front of the ultravioletlamp. The distance between adjacent partitions is set such that is notlarger than 30 cm.

The waste water W having passed through the ultraviolet treatment tank 9is once stored in a pH adjustment tank 10 in which slaked lime is thrownin for alkalization of the waste water W again.

After having passed through the pH adjustment tank 10, the waste water Wis transferred to a retention tank 11 which is comprised of anelectrolysis treatment tank for carrying out electrolysis and acarbonized filter medium treatment tank for effecting carbonized filtermedium treatment. The retention tank 11 is provided with a pair ofelectrodes 12 and 13 for use in carrying out electrolysis, and aplurality of carbonized filter mediums. The electrolysis treatment isexecuted mainly for eliminating harmful heavy metals, such as arsenic,cyanogen, aluminum, cadmium, and the like, which are originallyinoxidizable materials, from the waste water W. Electrolysis treatmentdevices are different from each other depending on kinds of harmfulheavy metals contained in the waste water W and hence required to beeliminated therefrom. This is because when waste water including onlyaluminum, manganese, or NaCl is to be treated, a less expensive andsimpler electrolysis treatment device is sufficient for treatmentthereof, than when waste water including more poisonous metals, such ascadmium, arsenic, organo-tin, etc, is to be treated. This embodimentemploys an electrolysis device capable of decomposing more harmfulsubstances such as cadmium.

The carbonized filter medium treatment is executed for eliminatingdioxins and the like which could not be decomposed completely by thepreceding treatments, or originally inoxidizable, harmful heavy metals,such as arsenic, cyanogen, aluminum, cadmium, and the like. Thecarbonized filter medium 14 and the water to be treated are brought intocontact with each other in the retention tank 11 in which 800 kg to12,000 kg of the carbonized filter medium 14 is used when the water istreated at the rate of 1 kiloliter per 1 minute. If the water is causedto stay in the retention tank 11 for a longer time period, it ispossible to reliably adsorb and eliminate the dioxins, the heavy metals,and other harmful substances. However, in order to carry out thecontinuous treatment as a characterizing feature of the presentinvention with efficiency, it is preferable to set a retention timeperiod to 30 minutes or shorter. In this embodiment, the retention timeperiod is set to 2 minutes, and as the carbonized filter mediums 14,there are used carbonized filter mediums of conifer wood, such as cedarwood, pine wood, Japanese cypress (hinoki) wood, and the like, which aremore excellent in adsorptive power than activated carbons. This isbecause when activated carbons are employed, it takes at leastapproximately one hour of a retention time period, and it is required tochange activated carbons for replacement in one year, whereas if coniferspecial carbonized filter mediums are used, 30 minutes of a retentiontime period is sufficient for the treatment, and moreover a time periodfor replacement can be prolonged to 5 years. Further, the conifercarbonized filter mediums 14 used in this embodiment are each formed bya mixture of cedar wood, pine wood, and cypress wood having microporesof 30 to 70 Å, 20 to 50 Å, and 10 to 30 Å, respectively, and they canadsorb a larger amount of harmful substance than activated carbons whichhave micropores uniform in size in a particular range. It should benoted that the conifer carbonized filter mediums 14 can be obtained bycarbonizing raw wood comprised of a plurality of kinds of conifer wood,such as cedar wood, pine wood, and Japanese cypress (hinoki) wood, athigh temperatures between 800° C. and 900° C.

The waste water W subjected to the above treatments acquires a waterquality satisfying 26 drinking water-suited water quality criteriadefined by the Japanese food sanitation law, and can be discharged tothe environment as water above a drinking water quality level. Even ifdischarged to the environment, the treated waste water does not containdioxins and the like, so that it is possible to break a vicious circleof poisonous substances. Further, the above-described treatments canextinguish all the bacteria and disease germs, including Escherichiacoli, as well as deodorize and decolorize the waste water.

According to the present embodiment, even when photocatalytic treatmentis not executed, it is possible to eliminate approximately 70% of thedioxins in the water to be treated only by the ozone treatment, and ifthe ozone treatment is carried out in combination with the ultravioletradiation treatment, approximately 95% of the dioxins can be eliminated.If the photocatalytic treatment is effected in combination with theozone treatment and the ultraviolet radiation treatment, approximately99% of the dioxins can be eliminated. If the electrolysis treatment andthe carbonized filter medium treatment are carried out together with theabove treatments, approximately 100% of the dioxins can be eliminated.Further, it is possible to decompose and eliminate environmentalhormones, such as PCB, nonyl phenol, nonionic surface active agents,etc, to values below the lower limit values of determinate quantitiesonly by carrying out the ozone treatment.

It should be noted that the advanced water treatment system of thepresent embodiment treats waste water W at a rate of 0.025 to 14kiloliters per minute.

Next, variations of the above embodiment will be described hereinafter.

The aeration tank suffers from the problem of a foul odor emitted fromhuman excreta thrown therein. To overcome this problem, a deodorizingline can be provided as a separate member for drawing in foul odorsstored in an upper portion of the aeration tank, transferring the samevia a pipe different from the pipes for sewage water and dischargingthem from a lower portion of the hydrogen peroxide treatment tank.

In the hydrogen peroxide treatment tank, at least one of gold, copperoxide, and iron oxide may be used as a pro-oxidant to promote oxidationby hydrogen peroxide solution. By throwing these pro-oxidants in thehydrogen peroxide treatment tank, the oxidizing action of the hydrogenperoxide can be promoted. If the pro-oxidants are not in use, they maybe lifted to the upper portion of the hydrogen peroxide treatment tank.

In the retention tank, similarly to the hydrogen peroxide treatmenttank, the upper portion of the tank may be coated with titanium dioxideand exposed to a fluorescent light to thereby deodorize foul odorsremaining in the upper portion of the tank by using the photocatalyticfunction of the titanium dioxide.

The method of generating minute bubbles of ozone for use in the ozonetreatment includes a revolving method, and a vortex turbine pump methodin addition to the line mixer method. The revolving method generatesminute bubbles of zone in water to be treated, by turning around ozoneand the mixture of the water to be treated by revolving blades orprojections. This method makes it possible to form ozone into bubbleshaving a particle diameter of 10 to 60 μm. Further, the vortex turbinepump method forms ozone into minute bubbles by the agitating power of aturbine pump. This method makes it possible to form ozone into minutebubbles having a particle diameter of 20 to 80 μm. In the line mixermethod, the particle diameter of minute bubbles of ozone is set to arange of 0.5 to 3 μm, in the revolving method, the particle diameter ofminute bubbles of ozone is set to a range of 10 to 20 μm, or 50 to 60μm, In the vortex turbine pump method, the particle diameter of minutebubbles of ozone is set to a range of 20 to 80 μm. In the revolvingmethod and the vortex turbine pump method, the above mentioned range ofparticle diameter is for the bubbles of ozone since if the particlediameter is larger an upper limit of a corresponding one of the aboveranges, treatment efficiency thereof is degraded, whereas if theparticle diameter is smaller than a lower limit of the same, themanufacturing costs of an ozone bubble-forming device are increased,resulting in the unfavorable relationship between the treating effectand the manufacturing costs.

Further, the rate of injection of ozone (amount of ozone brought intocontact with water to be treated) is determined depending on the amountof organic substances dissolved in the water to be treated and the like.In this variation, the rate of injection of ozone is set to 0.004 to0.0015 mg (4 to 15 ppm) per liter of water to be treated. If the rate ofinjection of ozone is smaller than 0.004 mg/liter, the effect ofinjection of ozone is reduced, whereas if the rate of injection ozone islarger than 0.015 mg/liter, the treatment efficiency per amount of inputozone is degraded.

The method of supplying minute bubbles of ozone to the ozone treatmenttanks are different depending on the type of ozone bubble-formingdevices. In the case of the vortex turbine pump method, the method isthe same as that of the line mixer method. That is, an ozone generatorfor generating minute bubbles of ozone is arranged in a water pipe tosupply water having minute bubbles of ozone dispersed therein to theozone treatment tanks. On the other hand, in the revolving method, thereis no ozone bubble-forming device arranged in a waste pipe. Ozonebubble-forming devices are arranged on bottoms of the ozone treatmenttanks for feeding minute bubble of ozone therefrom.

It should be noted that minute bubbles of ozone are almost instantlydiffused throughout the ozone treatment tanks regardless of whichevermethod may be employed. Therefore, the ozone treatment tanks may haveany shapes, such as a vertically long shape, a horizontally long shape,and the like.

In the waste ozone-disposal treatment, a waste ozone-disposal treatmenttank is arranged at an upper portion of a front-side tank of two ozonetreatment tanks communicating with each other, but it is preferable toexecute waste ozone-disposal treatment also in another wasteozone-disposal treatment tank placed at a latter-stage side of theultraviolet radiation tank. Further, it is possible to effectivelyutilize ozone to be disposed of, by transferring air remaining at theupper portion of the ozone treatment tank to the water storage tank forreceiving the human excreta and the like, for deodorization. In thiscase, a waste ozone-disposal treatment tank is arranged at an upperportion of the water storage tank for receiving the human excreta andthe like.

According to another embodiment of the present invention, in the watertreatment system of a fixed type shown in FIG. 1, the electrolysistreatment to be effected in the retention tank 11 is carried out betweenthe storage tank 4 and the ozone treatment tank 6. This makes itpossible to utilize remaining aqueous hydrogen peroxide to carry outelectrolysis efficiently.

FIG. 2 and FIG. 3 show another embodiment of the present invention. Itshould be noted that redundant description of component parts andelements which have been described above with reference to FIG. 1 willbe omitted. This embodiment shows an in-vehicle water treatment system.A large-sized truck 15 has a loading platform provided with a storagetank 16 for drawing in waste water W by vacuum. Reference numeral 17designates a vacuum generator for generating vacuum with which the wastewater W is drawn in. Reference numeral 18 designates a generator unit.

The waste water W in the storage tank 16 is sequentially transferred toozone treatment tanks 20 and 21 through a screen 19. In the case of thein-vehicle water treatment system, the “aqueous hydrogen peroxidetreatment tank” is omitted due to a narrow space of the loadingplatform, but the ozone treatment tanks 20 and 21 have enhancedcapabilities of ozone treatment. Each of the ozone treatment tanks 20and 21 includes an ozone generator 22 a, an ozone bubble-forming device22 b, and a waste ozone-disposal treatment device 23. After the wastewater W has passed through the ozone treatment tanks 20 and 21, it issent to an ultraviolet radiation tank 24, where harmful substancescontained therein are farther decomposed by ultraviolet rays.

The waste water W, having passed through the ultraviolet radiation tank24, is guided to a carbonized filter medium treatment tank 25. Thecarbonized filter medium treatment tank 25 has sand heaped up thereinfor removing solid components from the waste water W by filtration.Then, finally, the waste water W is transferred to a retention tank 26which has a plurality of carbonized filter mediums arranged therein. Thewaste water W is caused to stay in the retention tank 26 for apredetermined time period to adsorb harmful heavy metals for removaltherefrom, so that the waste water W is purified to a water qualitylevel suitable for drinking water, and hence can be discharged to theenvironment. In this embodiment, since the water treatment system is ofan in-vehicle type, it can move to any place as required to treat wastewater W.

Industrial Applicability

According to the present invention, harmful substances, such as dioxinsand the like, can be subjected to reliable oxidative destruction, andhence it is possible to break a vicious circle of toxic substancesthrough wastes from human bodies and industrial waste water.

What is claimed is:
 1. An advanced water treatment process for bringingminute bubbles of ozone into contact with water to be treated whichcontains harmful substances including dioxins and PCB to carry outoxidative destruction of the harmful substances contained in the waterto be treated, the advanced water treatment process comprising: mixingtogether ozone generated from an ozone generator and the water to betreated to obtain water to be treated which contains ozone; passing thewater to be treated which contains ozone through an ozone bubble-formingdevice arranged in a water pipe to obtain water to be treated whichcontains minute bubbles of ozone, bringing the minute bubbles of ozoneinto contact with the water to be treated; supplying to at least oneozone treatment tank the water to be treated which contains the minutebubbles of ozone; and carrying out oxidative destruction of the harmfulsubstances in the water to be treated.
 2. The advanced water treatmentprocess according to claim 1, wherein the minute bubbles of ozone havean average particle diameter of 0.5 to 3 μm.
 3. The advanced watertreatment process according to claim 1, wherein the minute bubbles ofozone have an average particle diameter of 20 to 80 μm.
 4. The advancedwater treatment process according to claim 1, wherein the at least oneozone treatment tank includes a plurality of ozone treatment tanksarranged at respective successive stages, such that waste ozone in alatter-stage one of the ozone treatment tanks is circulated to aformer-stage one of the ozone treatment tanks.
 5. The advanced watertreatment process according to claim 1, wherein prior to an ozonetreatment, or posterior to the ozone treatment, a hydrogen peroxidetreatment using a hydrogen peroxide solution is carried out for thewater to be treated.
 6. The advanced water treatment process accordingto claim 5, wherein prior to the treatment by using the hydrogenperoxide solution, the water to be treated is adjusted to a pH of 8 to10.
 7. The advanced water treatment process according to claim 1,wherein an ultraviolet radiation treatment is carried out for the waterto be treated after the ozone treatment, the water containing residualozone which did not act in the oxidative destruction of the harmfulsubstances.
 8. An advanced water treatment process for bringing minutebubbles of ozone into contact with water to be treated, which containsharmful substances including dioxins and PCB, thereby carrying outoxidative destruction of the harmful substances, wherein prior to anozone treatment, or posterior to the ozone treatment, a treatment byusing a hydrogen peroxide solution is carried out for the water to betreated and a foul-odor air generated from the water within a treatmentsystem is formed into minute bubbles such that the minute bubbles of thefoul-odor air are mixed into the hydrogen peroxide solution so that thefoul-odor air undergoes oxidative destruction.
 9. The advanced watertreatment process according to claim 8, wherein the minute bubbles ofthe foul-odor air have an average particle diameter of 0.01 to 0.02 mm.10. An advanced water treatment process for bringing minute bubbles ofozone into contact with water to be treated which contains harmfulsubstances including dioxins and PCB to carry out oxidative destructionof the harmful substances contained in the water to be treated, theadvanced water treatment process comprising: mixing together ozonegenerated from an ozone generator and the water to be treated to obtainwater to be treated which contains ozone; supplying the water to betreated which contains ozone to an ozone treatment tank, the ozonetreatment tank having an ozone bubble-forming device provided on itsbottom; and subjecting the water to be treated which contains ozone to aforced convection state within the ozone treatment tank to obtain waterto be treated which contains minute bubbles of ozone, bringing theminute bubbles of ozone into contact with the water to be treated. 11.The advanced water treatment process according to claim 10, wherein theminute bubbles of ozone have an average particle diameter of 10 to 20μm.
 12. The advanced water treatment process according to claim 10,wherein the minute bubbles of ozone have an average particle diameter of50 to 60 μm.
 13. The advanced water treatment process for bringingminute bubbles of ozone into contact with water to be treated, whichcontains harmful substances including dioxins and PCB, thereby carryingout oxidative destruction of the harmful substances, wherein at leastone of gold, copper oxide, and iron oxide is thrown into the water whichis to be subjected to the treatment by using the hydrogen peroxidesolution, thereby promoting an oxidation treatment by the hydrogenperoxide solution.
 14. An advanced water treatment process for bringingminute bubbles of ozone into contact with water to be treated, whichcontains harmful substances including dioxins and PCB, thereby carryingout oxidative destruction of the harmful substances, wherein prior tothe ozone treatment, an electrolysis treatment is carried out for thewater to be treated.
 15. An advanced water treatment process forbringing minute bubbles of ozone into contact with water to be treated,which contains harmful substances including dioxins and PCB, therebycarrying out oxidative destruction of the harmful substances andirradiating ultraviolet light, wherein irradiating ultraviolet lightincludes an ultraviolet radiation treatment tank is arranged within atreatment system, the ultraviolet radiation treatment tank having anultraviolet light source arranged therein and inner walls thereof coatedwith titanium dioxide, ultraviolet ray is irradiated onto the innerwalls to thereby cause a photocatalytic treatment for deodorizing afoul-odor within the ultraviolet radiation treatment tank.
 16. Anadvanced water treatment system for purifying water to be treated whichcontains harmful substances including dioxins and PCB, the advancedwater treatment system comprising: a water pipe through which the waterto be treated is introduced into an ozone treatment tank, the water tobe treated containing ozone generated by an ozone generator; and theozone treatment tank having an ozone bubble-forming device provided onits bottom, in which the water to be treated which contains ozone issubjected to forced convection to generate minute bubbles of ozone,effecting oxidization of the harmful substances contained in the waterto be treated.
 17. The advanced water treatment system according toclaim 16, wherein the ozone supply means forms ozone into minute bubbleshaving an average particle diameter of 50 to 60 μm.
 18. The advancedwater treatment system according to claim 16, wherein the ozone supplymeans forms ozone into minute bubbles having an average particlediameter of 10 to 20 μm.
 19. An advanced water treatment system forpurifying water to be treated, which contains harmful substancesincluding dioxins and PCB, the advanced water treatment systemcomprising an ozone treatment tank for bringing minute bubbles of ozoneinto contact with the water to be treated, thereby carrying outoxidative destruction of the harmful substances, including a hydrogenperoxide solution treatment tank at a water inlet side or a water outletside of the ozone treatment tank and including foul-odor supply meansfor forming a foul-odor air generated from the water within thetreatment system into minute bubbles such that the minute bubbles of thefoul-odor air are mixed into the hydrogen peroxide solution.
 20. Theadvanced water treatment system according to claim 19, wherein thefoul-odor supply means causes the minute bubbles of the foul-odor air tohave an average particle diameter of 0.01 to 0.02 mm.
 21. An advancedwater treatment system for purifying water to be treated which containsharmful substances including dioxins and PCB, the advanced watertreatment system comprising: ozone supplying means for introducing ozonegenerated by an ozone generator to a water pipe through which the waterto be treated passes, supplying minute bubbles of ozone obtained with anozone bubble-forming device provided in the water pipe; and at least oneozone treatment tank in which oxidation of the harmful substances iseffected by using the minute bubbles of ozone that are brought intocontact with the water to be treated.
 22. The advanced water treatmentsystem according to claim 21, including an ultraviolet radiationtreatment tank at an outlet side of the ozone treatment tank, theultraviolet radiation treatment tank having an ultraviolet light sourcearranged therein and inner walls thereof coated with titanium dioxide.23. The advanced water treatment system according to claim 21, whereinthe ozone supply means forms ozone into minute bubbles having an averageparticle diameter of 20 to 80 μm.
 24. The advanced water treatmentsystem according to claim 21, wherein the at least one ozone treatmenttank includes a plurality of ozone treatment tanks arranged atrespective successive stages, such that extra ozone coming up from thewater to be treated in a latter-stage one of the ozone treatment tanksis circulated to a former-stage one of the ozone treatment tanks. 25.The advanced water treatment system according to claim 21, including ahydrogen peroxide solution treatment tank at a water inlet side or awater outlet side of the ozone treatment tank.
 26. The advanced watertreatment system according to claim 21, wherein the ozone supply meansforms ozone into minute bubbles having an average particle diameter of0.5 to 3 μm.
 27. An advanced water treatment system for purifying waterto be treated, which contains harmful substances including dioxins andPCB, the advanced water treatment system comprising an ozone treatmenttank for bringing minute bubbles of ozone into contact with the water tobe treated, thereby carrying out oxidative destruction of the harmfulsubstances including an ultraviolet radiation treatment tank at anoutlet side of the ozone treatment tank, the ultraviolet radiationtreatment tank having an ultraviolet light source arranged therein andinner walls thereof coated with titanium dioxide, wherein theultraviolet radiation treatment tank has a plurality of partition wallscoated with titanium dioxide, the partition walls being arranged suchthat a distance between adjacent ones thereof is within 30 cm.
 28. Theadvanced water treatment system according to claim 27, wherein theultraviolet radiation treatment tank has a body in the form of abottomed hollow cylinder extending vertically, an ultraviolet lamp beingarranged in a diametrical center of the body, with the plurality ofpartition walls having plate surfaces radially extending toward theultraviolet lamp positioned in the center of the arrangement ofpartition walls.
 29. The advanced water treatment system according toclaim 28, including a carbonized filter medium treatment tank arrangedat a water outlet side of the ultraviolet radiation treatment tank, thecarbonized filter medium treatment tank having a conifer carbonizedfilter material obtained by carbonizing raw materials of plural kinds ofconifer, including cedar, pine, and Japanese cypress (hinoki) at a hightemperature range of 800 to 900° C.
 30. An advanced water treatmentprocess according for bringing minute bubbles of ozone into contact withwater to be treated, which contains harmful substances including dioxinsand PCB, thereby carrying out oxidative destruction of the harmfulsubstances, wherein an ultraviolet radiation treatment is carried outfor the water to be treated after the ozone treatment, the watercontaining residual ozone which did not act in the oxidative destructionof the harmful substances and after the ultraviolet radiation treatment,an electrolysis treatment and a carbonized filter medium contacttreatment are carried out for the water to be treated.